1. Technical Field
The present invention relates to a key switch structure, and in particular relates to a key switch structure employed in a keyboard where there is a strong demand for thinner models, for example in a portable personal computer or word processor.
2. Related Art
In keyboards employed in for example portable personal computers, configuration is made such that no matter where on the key top a key is depressed, the key top moves downwards without tilting, ensuring good operation characteristics. Existing key switch structures therefore have a link mechanism provided beneath the key top. Key switch structures exist with a link mechanism provided beneath the key top (see for example Japanese Patent No. 4341733).
Such key switch structures are configured with a key top 210, a first link member 220, a second link member 230, a holder 250, a membrane 260, a back plate 270, and a resilient member 240.
As illustrated in FIG. 9 and FIG. 10, the above key switch structure is a structure provided with a configuration in which the key top 210 descends whilst maintaining a horizontal state due to a link mechanism in which two link members 220, 230 are assembled together in an X-shape.
A first support projection 224 on the first link member 220 is rotatably supported by rotation support members 214 at a rear side of the key top 210, and first support projections 234 on the second link member 230 are similarly rotatably supported by rotation support members 254 on the holder 250. Thus second support projections 222, 232 provided to the other respective ends of the link members are supported so as to be capable of sliding by slide support members 256, 212 provided to the holder 250 and the key top 210, respectively.
When the key top 210 has been depressed, the resilient member 240 deforms in a squashing direction, deforming towards the membrane 260, whilst the link members assembled together in an X-shape cause the second support projections 222, 232 to slide. The key top 210 consequently descends whilst maintaining a horizontal state.
A projection 252 provided to the holder 250 passes through a hole 262 in the membrane 260 and a hole 272 in the back plate 270, and a leading end is positioned and fixed with respect to the back plate 270 using a method such as welding.
However, when fabrication accuracy for the back plate 270 and the holder 250 is poor, and/or the accuracy when welding together the two components is poor, gaps can develop between the back plate 270 and the holder 250. There is also the possibility of the second support projection 222 (slide section) of the first link member 220 moving up and down, namely in the key top depressing direction, giving rise to a wobbling sensation during depressing as the key top 210 is unable to maintain a horizontal state.
If for the sake of convenience the holder 250 is formed as a single unified component including the rotatable support sections 254 and the slide support section 256, and the resilient member 240 is disposed directly below the center of the key top 210, there will inevitably be a thinned portion present in a portion of the link member due to the first link member 220 having a profile enclosed from the periphery by the holder 250. Accordingly force is concentrated at this thinned portion when load is applied during depressing the key top 210, giving rise to a wobbling sensation.
Even in cases where the back plate 270 is provided with an up stand into which the second support projection 222 is fitted, when the fabrication accuracy is low the link member (the second support projection 222 and the first support projections 234) will give rise to a wobbling sensation due to not being disposed correctly.
In the above structure disclosed in Japanese Patent No. 4341733, depending on the fabrication accuracy there is a concern that a sensation of insufficient rigidity during operation, referred to as a wobbling sensation, will be caused by lowering of the positional accuracy of the link member, or due to force being concentrated at thinned portions present in the link member.